I know this is late, but, wanted to confirm, that while many said it could be 5th disease (I think that is the "slapped face" one... which is NOT bumpy on the tummy first...) kids CAN exhibit allergic reactions after being on something for a few days. My daughter did this at about 9 months after taking Omnicef for 3 1/2 days. I was stunned, b/c I had always thought that if you were allergic you broke out (or whatever the reaction) pretty much right away (within 12-24 hrs). But our doc said she is not allergic, but had a "hypersensitivity" to it... it takes a few days for the body to get enough in the system to react to it. Our daughter was put on another medication for the infection we were trying to treat, and took a prednisone type drug to counteract the allergic reaction (she started with tiny bumps on arms and belly, then red splotches came... welts were not far behind... the Dr warned us she would look bruised all over before she was fully "recovered" from it, and she did show some bruising, but not as bad as I'd heard it could be.)... Don't discount that she could in fact have a reaction after being on it for several days...